The ability to measure surface characteristics of flat panel displays has become more challenging as the size of the displays increases with evolving technology. The most common type of flat panel display is essentially a multi-layer sandwich of 0.7 mm thick glass sheets, plus mechanical support structure and electronics to address the pixels in the display. Until recently, the largest flat panels being fabricated were approximately 650 mm long. Today, however, there are a number of plants preparing to produce larger panels having dimensions up to 1100 mm long by 800 mm wide.
During production of flat panel displays, an accurate surface profile is required. Profiling entails measuring and mapping surface steps and irregularities across the panel. If the surface steps are the wrong height, or irregularities are sufficiently large, the panel must be rejected.
Emerging State-of-the-art large panels present difficulties for the prior art surface profilers which were originally designed to profile silicon wafers sized less than 200 mm in diameter. In most of the prior art designs, the measurement head was held stationary while the sample was moved beneath the stylus. Another prior art profiler design is described in U.S. Pat. No. 4,391,044 to Wheeler, entitled "Metrology Instrument for Measuring Vertical Profiles of Integrated Circuits and the Like," which is incorporated by reference herein. This profiler was designed for small samples, such as silicon wafers and other electronic components, but cannot measure large samples, such as 1 m flat panel displays.